Conventionally, there is known a substrate processing apparatus configured to process a substrate by supplying a processing liquid onto a substrate such as a semiconductor wafer from a nozzle disposed above the wafer (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Laid-open Publication No. 2008-118109
In this kind of substrate processing apparatus, after a discharge of the processing liquid is stopped, there may be performed a process (hereinafter, referred to as a “withdrawing process”) of withdrawing a liquid surface of the processing liquid remaining within the nozzle in order to suppress the processing liquid from dripping down from the nozzle.
Here, in order to check whether the withdrawing process has been performed properly, a position of the liquid surface within the nozzle may need to be observed after the withdrawing process. If, however, the nozzle is made of a material including an opaque material such as a metal as in the case of the nozzle disclosed in Patent Document 1, for example, the inside of the nozzle cannot be seen from the outside, and it is difficult to check the position of the liquid surface within the nozzle.